Chair base



FIG. 1 is a front perspective view of the chair base in accordance with the present invention;

FIG. 2 is a top view thereof;

FIG. 3 is a bottom view thereof;

FIG. 4 is a left side view thereof;

FIG. 5 is a right side view thereof;

FIG. 6 is a back view thereof; and,

FIG. 7 is a front view thereof.

The portions of the drawings shown in broken lines are shown for environmental purposes only and form no part of the claimed design. 

The ornamental design for chair base, as shown and described. 